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Old 11th Mar 2019, 10:33 am   #1
bugbear
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Default ITT-KB Weekend Automatic - distortion?

I just got this neat little radio (destined for the Kitchen shelf).

It's essentially clean, and works well.

But at anything other than quite low volume there's a lot of distortion.

Is this simply a limitation of the product/design or "other?

My personal suspicion, based on limited knowledge, is that the smoothing capacitors in the main PSU aren't supplying a solid voltage.

Diagnoses, or pointers to diagnostic techniques, welcomed.

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Old 11th Mar 2019, 12:52 pm   #2
orbanp1
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Default Re: ITT-KB Weekend Automatic - distortion?

Hi BugBear,

Chances are the final audio amp in the radio is off.
RM has the schematics:
https://www.radiomuseum.org/r/itt_we...automatic.html

Do check if the common emitter point of the final transistors (CS1909, CS1910) are indeed at half the supply voltage (DC), and continue from there.

Regards, Peter
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Old 11th Mar 2019, 1:43 pm   #3
crackle
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Default Re: ITT-KB Weekend Automatic - distortion?

Like all ITT-KB radios, distortion is not normally a feature. Don't rule out checking the speaker for rubbing or loose diaphragm inner support.
The ITT Service information is also on the KB Museum website, it includes a printed circuit layout to help you locate the components. http://www.kbmuseum.org.uk/itt_servi...omatic_ITT.pdf
Good luck, they sound good when working correctly.
Mike
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Old 11th Mar 2019, 7:23 pm   #4
buggies
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Default Re: ITT-KB Weekend Automatic - distortion?

The circuit shows a battery/mains switch - so that should quickly eliminate the power supply.
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Old 11th Mar 2019, 8:29 pm   #5
rambo1152
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Default Re: ITT-KB Weekend Automatic - distortion?

First think I'd suspect with distortion at low volume, is an out-of-centre speaker cone
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Old 15th Mar 2019, 3:07 pm   #6
bugbear
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Default Re: ITT-KB Weekend Automatic - distortion?

Thanks for the practical suggestions; a quick go with a set of batteries, and wiring external speakers via the headphone socket should answer some questions, at least for starters.

BugBear

Last edited by bugbear; 15th Mar 2019 at 3:13 pm.
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Old 19th Mar 2019, 10:53 am   #7
bugbear
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Default Re: ITT-KB Weekend Automatic - distortion?

Oddly, the radio has simply "settled in" and is now behaving much better.

I note that the RM website doesn't have a "covers off" photo of the innards. Would they like one (I took one for my own purposes) ?

https://farm8.staticflickr.com/7808/...31ec5037_b.jpgle_weekend by plybench, on Flickr

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Old 19th Mar 2019, 7:28 pm   #8
crackle
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Default Re: ITT-KB Weekend Automatic - distortion?

I think possibly an electrolytic capacitor has reformed, this can happen sometimes. I have had radios which dont work at all then after a little while they slowly start to work, and often they continue to improve over the next 30 minutes or so.
Thanks for the photo of the insides. https://www.radiomuseum.org/r/itt_we...automatic.html

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